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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Samyan on August 25, 2020, 12:42:03 PM

Title: Solubility Equilibrium
Post by: Samyan on August 25, 2020, 12:42:03 PM
If the ion concentration of two ions in a reaction are different how will they reach equilibrium?
like in CaSO4  ::equil:: Ca2+ + SO4 2- if the calcium ion concentration is 0.04M and the sulfate ion concentration is 0.01 M and at equilibrium the ion concentration for both is 4.99x10-3 M how would they both get to the same concentration??
Title: Re: Solubility Equilibrium
Post by: Meter on August 25, 2020, 01:30:22 PM
Since the initial calcium ion concentration is higher,  the reaction will shift to favor the formation of more sulfate ions in order to reach an equilibrium.

My guess would be that the excess calcium ions would then precipitate as the solution becomes saturated. I am not 100% sure though.
Title: Re: Solubility Equilibrium
Post by: Corribus on August 25, 2020, 02:40:02 PM
Common mistake: Equilibrium does not mean the concentrations of the products are the same.
Title: Re: Solubility Equilibrium
Post by: Meter on August 25, 2020, 02:47:44 PM
Quote from: Corribus on August 25, 2020, 02:40:02 PM
Common mistake: Equilibrium does not mean the concentrations of the products are the same.
But wouldn't it be the case in this situation as CaSO4 has 1 mol Ca2+ and 1 mol SO42-?
Title: Re: Solubility Equilibrium
Post by: Corribus on August 25, 2020, 04:30:54 PM
Maybe it is best to start with what the actual wording of the problem is, so that we can make sure we are answering the same thing.
Title: Re: Solubility Equilibrium
Post by: Enthalpy on August 26, 2020, 04:33:05 AM
Quote from: Meter on August 25, 2020, 01:30:22 PM
My guess would be that the excess calcium ions would then precipitate as the solution becomes saturated. I am not 100% sure though.
Neither am I...
Title: Re: Solubility Equilibrium
Post by: Enthalpy on August 26, 2020, 04:39:56 AM
Quote from: Samyan on August 25, 2020, 12:42:03 PM
If the ion concentration of two ions in a reaction are different how will they reach equilibrium?
Like in CaSO4  ::equil:: Ca2+ + SO42- if the calcium ion concentration is 0.04M and the sulfate ion concentration is 0.01 M and at equilibrium the ion concentration for both is 4.99x10-3 M how would they both get to the same concentration?

If the amounts of calcium and sulphate differ, more reactions matter in an equilibrium, for instance the presence of OH-. Electrical neutrality.

So an equilibrium involves several reactions then. The resulting pH probably influences the equilibrium constant for the dissolution of CaSO4. Not an easy start.

Yes, the actual wording is needed.